Chloride Limits in the ACI 318 Building Code Requirements

After much debate, a table showing maximum chloride ion contents for different types of concrete members first appeared 15 years ago in ACI 318-83, "Building Code Requirements for Reinforced Concrete." That original table hasn't changed and will remain unchanged until at least 2001 since ACI Committee 318 recently decided not to adopt proposed revisions that would have reduced most of the maximum values. But the debate continues over proper values for the limits.ACI 222R-96, "Corrosion of Metals in Concrete," recommends lower maximum values, basing its case primarily on a comparison of the chloride-content limits currently in ACI 318-95 with a value called the chloride corrosion threshold.Throughout the debate, opponents of the more stringent chloride limits have argued that there has been little evidence of corrosion problems traceable to the chloride limits in place since 1983.Change proponents, however, argue that while the use of calcium chloride could be limited by adoption of lower values for the maximum chloride-ion percentages, many specifications already ban any admixture with intentionally added chlorides when chloride content is an issue. Change proponents also argue that ACI 318 doesn't apply to soil-supported slabs, in which chlorides are now typically used as accelerators, unless the slab transmits vertical loads from other portions of the structure to the soil.Two facts are certain in this chloride-limit argument. First, ACI 318 will revisit this issue in the near future as it prepares for the 2001 edition of its code requirements. Second, the Soxhlet method will ultimately be accepted for use, paving the way for a performance focus on chloride limits.The article includes two tables on water-soluble chloride-ion limits in ACI 318-95 and chloride limits for new construction proposed by ACI 222. It also describes differences in test methods and tells how to submit chloride-test results.